It is not free. You HAVE to pay $1.99 or the game is unplayable due to the ads. They used to be practically nothing, just small images that could be closed. Now, they are videos with "try me!" attached to the end, which can take upwards of 20 seconds to get through. Now, 20 seconds is nothing, right? Wrong. Later in the game, your rhythm is very important. You need to have a flow and understand when to press, how long to press, etc. When you have an ad after every other death (which is a lot, because you die a lot. A lot.), it is practically impossible to fix.
I have had this game installed since the beginning, and didn't pay for ads to be removed until recently. I never had a reason to. Now, it is unplayable, especially later in the game, without paying for ads to be removed. Just accept you have to pay $1.99, and you'll be happy. If you're looking for a free ride, you're not going to be happy. I'd recommend their new game, Mr. Jump S, if this game proves to be too much with the ads, and you're unwilling to buy.
To the dev: I understand you need to make money, but I humbly request you either reduce the cost of "Remove Ads", or you make them less intrusive. I love this game and I have no issue supporting you, but making the game unplayable without doing so is crooked. Just make it $1.99 and put no ads if you want the money so badly.